Ohmic probe integration for IoSender and grblHAL

[DBS3262]

This is a strategy for detecting material surface position with the a ohmic sensor, or float switch using the same probe input. The ohmic sensor is the primary means of detection, with the float switch serving as a backup. It's completely programable from g-code, and doesn't interfere with other types of surface probing if you're also occasionally running a spindle on the same table.

How the hardware works.......

Ohmic Detection

1. When the ohmic sensor touches metal, the NO contact on the ohmic sensor closes. This will energize the DPDT relay.
2. This applies a ground signal to the AuxIn and Probe pins through the NO contacts which are now closed. This pulls Probe pin LOW, signals material detection, and stops further movement. Based on logic in macro, AuxIn LOW is identified as Ohmic Probe and the appropriate offset is used.
3. Torch moves to pierce height and ohmic sensor opens contacts releasing DPDT relay. Probe and AuxIn pins return to HIGH state.

Float switch Detection

1. Ohmic sensor failed to trigger. Controller is blind to material and continues to plunge torch into material.
2. Float switch (NPN NC proximity switch) triggers, sending ground signal through NC contact on DPDT relay to probe pin. This pulls probe pin LOW signaling detection and stops further movement. Based on logic in macro, AuxIn HIGH, is identified as float switch and the appropriate offset is used.
3. Torch moves to pierce height and ohmic sensor opens contacts releasing DPDT relay. Probe and AuxIn pins return to HIGH state.

Here's the wire diagram for the hardware:

OhmicProbeWireDiagram.pdf

The Macro.......

If you're unfamiliar with G65 Macros, I would advise you to first visit the SD Card Plugins and Expressions and Flow Control pages to get a basic understanding of macros and what changes you'll need to make to your firmware.

My basic probe macro is below. I prefer to limit the macro to probing and offset selection. You will need to adjust the offsets to match your tables parameters.

`;M66P221

#1 = 0.000 ;OHMIC OFFSET ADJUST AS REQUIRED
#2 = -4.500 ;FLOAT OFFSET ADJUST AS REQUIRED
;TEST HARDWARE TO ENSURE A FAULT IS NOT PRESENT
M66P0L0 ;LOOK AT AUX IN 0 NOW
o100 IF[#5399 EQ 0] ;IF AUX IN 0 IS LOW
(ABORT, CHECK OHMIC PROBE FOR GROUNDED SENSOR OR STUCK RELAY)
o100 ENDIF
G38.2 Z-40 F100 ;BEGIN PROBE
M66P0L0 ;LOOK AT AUX IN 0 NOW
o101 IF [#5399 EQ 0] ; IF AUX IN 0 IS LOW OHMIC RELAY TRIGGERED
G10 L20 P#5220 Z#1 ;SET OHMIC OFFSET
o101 ELSEIF [#5399 EQ 1] ;IF AUX IN 0 IS HIGH FLOAT SWITCH TRIGGERED
G10 L20 P#5220 Z#2 ;SET FLOAT OFFSET
o101 ENDIF
M99 ;END MACRO`

Testing the macro from the MDI.
When the macro runs from the MDI it applies the offset and stops. Your torch will remain in the trigger position allowing you to observe any diagnostic LEDS, and the applied offset will be displayed in the DRO. You can repeat the test with a sheet of paper between the ohmic shield and metal. This time you should see the float LED trigger LED and the float offset in the DRO.

Lastly, Post processing ......
You are going to call your macro on all plunge moves. You'll also need to add the necessary cut parameters. G-code should look a little something like this:

G65P221 ;CALL MACRO
G1 Z3. ; MACRO HAS FINISHED MOVE TO PIERCE HEIGHT
M3. ; TURN TORCH ON
G4P0.4. ; DWELL FOR PIERCE
G1Z1.5. ; MOVE TO CUT HEIGHT

There are several ohmic sensors available. The Ohmic Pro from Proma Electronics and Kemo water switch will work well for the application.